Integrated ultra-thin silicon membrane for DM optical mirrors

Project context

Adapatative Optics (AO) requires fast and precise wavefront control using deformable optical surface (DM) with a large number of actuators. Current commercial DM technologies are efficient but still suffer from limitations in their temporal bandwidth, dynamical range, size, number of actuators, fragility/fatigue, and non-linear effects that need to be overcome for future instruments. Moreover, these DMs have unperfect shape at rest and are costly. We aim to develop a new hybrid high-speed, lightweight, large and low-cost deformable-mirror technology. This will lead to new cost-effective and lightweight opto-electronic systems that will be game changing for exoplanets studies with the ELTs.

FlexSiMirror is a inter-disciplinary project aimed at developing a new generation of deformable mirrors (DM). FlexSiMirror is the result of a consortium composed of 3 laboratories: the CRAL (Optics Metrology, UCBL) which is leading the project, the LGEF (Electroactive Materials and Additive Manufacturing, INSA Lyon) and the CMP (Silicon wafer technology electrode inks and additive manufacturing, Mines Saint-Etienne). The novelty of the instrument is to combine additive manufacturing of electroactive polymers and a self- supported silicon membrane technology. As part of this project, we will develop and optimize the state processes to fabricate defects-free and self-supporting silicon membranes. We will also develop a disruptive technology not using standard ceramics but rather EAP to produce, at higher temporal bandwidth, large and very accurate displacements compliant with the needs of future instruments. EAPs are easier and much cheaper to manufacture than conventional material because they are fabricated at relatively low temperatures and are fully 3D printed. The new EAP will be optimized to perform at high frequency (1 to 3kHz).. This new technology will lead to the mass-production of high quality DMs with significantly lower areal mass density (x50), larger number of actuators (x30) and significantly shorter production time and lower cost (x20) compared to conventional technologies. Its high performance will enable new instrumental concepts and will have many transverse applications for optical communications, high power laser beam shaping, space surveillance, remote sensing from space, medical imaging and industrial inspection – it opens the door to a new world of high-end, fast deformable optical systems.

Research objectives of the PhD

The aim of this thesis is the development and characterization of innovative ultra-thin larg area silicon membrane technology supported by EAP actuators. Only few papers reported in literature mentioned the use of such silicon membrane technology for conventional DM optical mirrors [1, 2]. However, the integration and processing of these reported technics are still difficult as it require different steps based on the use of strong acid such as HF (Hydrofluoredric acid) to etch the sacrificial layer used to support the silicon membrane. We can also mention that these reported processes are not compatible with the additive manufacturing process and the use of organic actuators targeted by the Fleximirror project. Thus, a new technology of manufacturing ultra-thin silicon membrane compatible with additive manufacturing process is required and it will present a novelty in the field of DM optical mirrors technology:

- Methods of fabricating of ultra-thin silicon membrane

- Microstructural and mechanical characterization of silicon membrane.

- Design and integration of embedded strain sensor

- Participating in the integration of full DM optical mirror 

Key words: Materials science, mechanic of materials, additive Manufacturing, , System integration, Finite element modeling simulations, Multiphysics characterizations (electrical, mechanical, thermic, couplings, etc.), Structure relationship properties

The FEL department of the CMPGC (Centre Microélectronique de Provence Georges Charpak / Ecole des Mines de Saint-Etienne (EMSE)) is composed of 8 permanent staff and a dozen PhD students and post-docs. The research activities aim to realize original electronic functionalities (transistors, sensors, batteries, triboelectricity, RFID, etc.) on flexible and stretchable media. Skills range from flexible electronic system design, printed electronics and materials. These are studied and developed while integrating the notion of mechanical flexibility. He was a pioneer in the additive printing of functional polymers such as PVDF and PEDOT :P SS. In this sense, the department has significant resources for additive manufacturing (clean room - ZRR and laboratories), the physical characterization of materials and devices, in particular the in-situ characterization of electrical properties under mechanical or thermal stress.The CMPGC, through the EMSE, has been labelled as the M.I.N.E.S Carnot Institute (Innovative Methods for Business and Society) since 2006.

You are a graduated engineer or master in materials science or applied physics, or mechanical engineering with a curiosity for new technologies.

•           You have a skill in multi-physics coupling, a good practical sense and knowledge and understanding of technological processes.

•           Knowledge in polymer physics and/or additive manufacturing would be helpful, but not mandatory

•           You are recognized for your autonomy, your curiosity, your versatility and your ability to learn.

•           You are able to develop quality relationships for the benefit of the advancement and progress of the activity at the internal level.